Zooplankton are a diverse group of tiny animals that float freely in the water column and feed on phytoplankton (plant plankton) and other zooplankton. This group includes jellyfish and comb-jellies, small crustaceans like copepods and krill, the larval forms of crabs and oysters, the larval or juvenile forms of some fish, and many other organisms. This Vital Sign tells us about the abundance and distribution of zooplankton populations in Puget Sound. Zooplankton play a critical role in the marine food web as important prey for juvenile salmon and small forage fish.